Mexico has written to China\'s Ministry of Commerce to complain about unfair practices by some of its exporters and threatened future trade reprisals, the economy minister said Wednesday.\"The letter is accompanied by proof and specific cases\" which threaten free trade,\" Bruno Ferrari told a news conference in Mexico City with representatives of industries including textiles and electronics. \"We\'re calling on the Chinese authorities to put companies that are using (unfair) practices in order.\"Ferrari criticized the trading of Chinese products via third nations to evade rules on bilateral exchange and the declaration of products at low prices that failed to cover the cost of their raw materials. The president of the National Clothing Industry, Marcos Cheren, said the price of some Chinese products even failed to cover shipping costs from Asia. \"Nine of every 10 dollars of clothes that China exports to Mexico enter illegally,\" he added, referring to a report by the Service of Tax Administration. Ferrari underlined that a World Trade Organization (WTO) clause which prevents Mexico from imposing sanctions on Chinese companies would expire in December. At that point, \"we\'ll be extremely virulent in our response if we don\'t have a reply from the Chinese authorities.\" China is the second largest exporter to Mexico after its main partner and neighbor the United States.Chinese exports to Mexico represented some 45 billion dollars last year, according to the economy ministry.